J. Org. Chem. 1981,46, 3-8
+
440 (M' 2,8), 438 (M', 8), 299 (26), 175 (92), 167 (33), 155 (87), 148 (96),41 (100). Anal. (CzoHzaBrO6) C, H. y-Lactone 13. A mixture of crude keto acid 6 (55 mg, 0.15 mmol) and triphenylphosphine (50 mg, 0.15 mmol) in 5 mL of carbon tetrachloride was first heated at 45 "C for 24 h and then at reflux for 6 h. Solvent was then removed in vacuo to give a foamy residue, which was dholved in ether and saturated sodium bicarbonate. After the layers were separated, the organic fraction was dried (MgS04)and then concentrated to give an oil. This was chromatographed on a 20 X 20 X 0.1 cm silica gel plate with 25% ethyl acetate in hexane as solvent. y-Lactone 13 was isolated (48 mg, 87%) as an oil which crystallized on storage. Recrystalliition from methylene chlorideheptane gave white needles: mp 126-128 OC; NMR (CDC13)6 0.82 (d, 3, J = 7 Hz); 0.96-1.70 (m, 7), 1.90-2.20 (m, l),2.53 (br s, 2), 2.51-3.20 (m, 3), 3.62 (8, 3), 6.00 (8,2), 6.59 (d, 1, J = 8 Hz), 6.62 (br s, l),6.80 (d, 1, J = 8 Hz); IR (CHC13) 1785,1740,1515,1500,1455,1260cm-'; mass spectrum (70 eV), m l e (relative intensity) 360 (M', 7), 176 (20), 162 (91, 149 (321,148 (100). Anal. (C&IUrOs) C, H. 2-Methoxy-5~-methyl-4~-(3,4-(methylenedioxy)phenyl-6propylcyclohepta-2,6-dienone (15). A solution of the bromo y-lactone 12 (439 mg, 1 mmol) and 0.5 N potassium hydroxide (16 mL) in tetrahydrofuran (10 mL) was stirred under an argon blanket for 1 h and then diluted with brine. The aqueous mixture was extracted thoroughly with ether; the ethereal solution was dried (MgS04)and evaporated in vacuo to give 271 mg of oily enol 14: NMR (CDC13) 6 3.76 (d of d, 1, J = 4 Hz, 9 Hz); IR (CHC13) 3400, 1645, 1600 cm-'; mass spectrum (70 eV), m l e (relative intensity) 300 (M', 16), 135 (100). The crude product was dissolved in 7 mL of dimethylformamide and to this was added excess silver(1) oxide (0.8 g) and methyl iodide (1 mL). The resulting suspension was stirred vigorously at room temperature for 20 h; insoluble materials were filtered and washed thoroughly with ethyl acetate and water. After the layers were partitioned, the organic phase was washed three times with water and then dried (MgSO,). Removal of solvent gave a pale oil. Filtration through a short column of silica gel with 25% ethyl acetate in hexane gave dienone 15 (213 mg, 68% from 12) as an oil which crystallized on storage. Recrystallization from ether-hexane gave an analytical sample: mp 75-77 "C; NMR
3
(CC14)6 0.69 (br t, 3, J = 7 Hz), 0.81-1.22 (m, 2), 1.33 (d, 3, J = 7 Hz), 1.84 (br t, 2, J = 7 Hz), 2.40-2.73 (m, 11, 3.62 (8, 31, 3.66 (d of d, 1, J = 4 Hz,9 Hz,one set is undemeath the methyl signal), 5.42 (d, 1, J = 9 Hz), 5.81 (br s, l),5.93 (8, 2), 6.64 (br s,3); IR (CHC13)1655,1640,1510,1495,1260 cm-'; W (95% EtOH) 255 nm (e 11 900), 283 (6500) 315 (sh, 3100); mass spectrum (70 eV), m l e (relative intensity) 314 (M', 69), 300 (lo),299 (49), 271 (28), 175 (100). Anal. (ClsH2204) C, H. 2-Methoxy-5-methyl-4-(3,4-(methylenedioxy)p heny1)-6propyltropone (17). A mixture of the dienone 15 (43 mg, 0.137 "01) and 2,3-dichloro-5,6-dicyano-l,4be~uinone(37 mg,0.16 mmol) in dry benzene (8 mL) was heated at reflux for 6 h under an atmosphere of nitrogen. After the mixture cooled, ether was added and the solution was washed successively with saturated sodium bicarbonate and brine and then dried (MgSO,). Evaporation of the solvent gave an oil which was chromatographed on a 20 X 20 X 0.1 cm silica gel plate with 50% ethyl acetate in methylene chloride as solvent. Pure tropone 17 (33.9 mg, 80%) was isolated as an oily solid. Crystallization from ether-hexane-methylene chloride gave small plates: mp 148-50 OC; NMR (CDC13)6 1.02 (br t, 3, J = 7 Hz), 1.46-1.80 (m, 2), 2.09 (s,3),2.62 (br t, J = 7 Hz), 3.84 (8, 3), 6.07 (8, 2),6.58-6.73 (m, 3), 6.90 (d, 1, J = 8 Hz), 7.30 (8, 1); IR (CHC13) 1605,1595,1560,1510, 1500, 1480,1440,1245,1200 cm-'; UV (95% EtOH) 248 nm (c 35000), low),348 (11600);maas spectrum (70 eV), m / e (relative 320 (8, intensity) 312 (M', 47), 285 (211, 284 (100). Anal. (ClsHmO4) C, H.
Acknowledgment. We thank the National Institutes of Health (GM 09868) and the Hoffmann-La Roche Foundation for financial support. High-resolution mass spectra were provided by the facility, supported by the National Institutes of Health (Grant RR 00317; principal investigator, Professor K. Biemann) from the Biotechnology Resources Branch, Division of Research Resources. Registry No. 3, 75522-10-0;4,67271-93-6;5, 120-58-1;6,7552211-1; 7, 75522-12-2;8,75522-13-3;11,75522-14-4;12,75522-15-5;13, 75522-16-6; 14, 75533-61-8; 15, 75522-17-7; 17, 75522-18-8; 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, 84-58-2.
Synthetic, Structural, and Chemical Study of the 1,2-Diphosphetene Ring Claude Charrier,'" Jean Guilhem,lb and Frangois Mathey*'" Laboratoire CNRS-SNPE, 94320 Thiais, France, and Institut de Chimie des Substances Naturelles, 91190 Gif-Sur-Yuette, France Received May 15, 1980
Synthesis of the diphosphetene ring by reaction of substituted acetylenes with cyclopolyphosphines was reinvestigated. In addition, a conversion of triphospholenes into diphosphetenes by lithium cleavage followed by ring closure with phosgene was devised. Thus, the two first alkyl-C-substituteddiphospheteneswere obtained. The X-ray crystal structure of tetraphenyldiphospheteneis described. No cyclic delocalization takes place within the ring. The cyclic strain is probably minimized owing to a P-P bent bond and a predistorsion of the C = C double bond geometry by the bulky C substituents. Some reactions of tetraphenyldiphosphetene are also described including their ring cleavage by lithium and their complexation by iron carbonyls. At 150 OC, Fs(CO), and Fe3(CO)12 cleave the P-P bond to yield a phosphido-bridged LFe2(CO)6complex through an intermediate complex of unknown structure. An excess of iron carbonyl then causes expulsion of the tolane subunit and gives a previously described phenylphosphinidene complex, (PhP)2[Fe(C0)3]3.
Among the various carbon-phosphorus monocyclic compounds known up to now only a few possess a 6aelectron system capable of giving rise to a cyclic delocalization. Phospholes and phosphorins have been studied in depth mainly in view of their possible aromaticity. On (1) (a) Laboratoire CNRS-SNPE. (b) Institut de Chimie des Substances Naturelles.
the other hand, practically nothing is known about the chemistry of the 1,2-diphosphetene ring 1 in spite of its discovery in 1964.2 In fact, only two such compounds are known where R = R' = CF, (la)2and R = R1= Ph (lb).3 Besides this, a brief study has appeared on the metal (2) W. Mahler, J. Am. Chem. Soc., 86, 2306 (1964). (3) A. Ecker and U. Schmidt, Chem. Ber., 106, 1463 (1973).
0022-3263181/ 1946~OO03$01.00/0 0 1981 American Chemical Society
4
J. Org. Chem., Vol. 46, No. 1, 1981 R'
R'
l a , R = R' = CF, b, R = R' = C,H, c, R = C,H,; R' = C,H, d, R = C,H,; R' = H e , R = C,H,; R' = t-C,H,
R'
Charrier, Guilhem, and Mathey Table I. Reaction of Tolane with (PhP), yield, %
R'
'c=c'
exptl conditionsa 150 OC, 72 h 180 OC, 72 h 240 OC, 6 h 280 OC, 5 h
I
R
2a, R = R' = CF, b, R = R' = C,H, C , R = C,H,; R' =C,H, d, R = C,H,; R' = H e , R = C,H,; R' = t-C,H,
Results and Discussion Synthesis. According to Ecker and SchmidtPsthe reaction of pentaphenylcyclopentaphosphine with tolane around 155-170 OC gave lb isolated as such in 11% maximum yield together with pentaphenyl-1,2,3-triphospholene (2b) isolated as ita 1,3-disulfidein 5.5% yield and 1,2,3,4,5-pentaphenylphosphol-3-ene (3) isolated as ita 1-oxide in ca. 0.5% yield.
Ph
Ph
4
As a first step we have reinvestigated this reaction at various temperatures and for various ratios of (PhP)5and tolane. Our results were quite different from those of Ecker and Schmidt. Some of them are collected in Table I. Our main product was always 2b isolated as such in yields as high as 75%. The diphosphetene lb was isolated in 15% maximum yield and the only recovered byproduct was pentaphenylphosphole4 which was fully characterized after isdation in ca.2-3% yield. The phosphole was easily detected on a TLC sheet by its strong fluorescence under W. In our opinion the 1,2,3,4,5-pentaphenylphosphol-3ene 1-oxide isolated by Ecker and Schmidt did not result from the oxidation of the corresponding tervalent phospholene 3, the formation of which would be very difficult to explain, but from the hydration of pentaphenylphosphole 4. Indeed, such hydrations have been described previously in the l i t e r a t ~ r e . ~ We then decided to check the scope of this synthesis of the diphosphetene ring by studying the reaction of (PhP), with some alkyl-substituted acetylenes. At 170 "C for 48 h, the reaction of (PhP), with t-BuCW-t-Bu gave the expected diphosphetene l e in 30% yield (eq 1). The
110 ' C
(PhP)6+ R ' C e R ' 1 +2 R' = t-Bu: le, 30%; 2e,O% R' = Et: IC, 0%; 2c, 36%
2b
0 0 15 2
50 75 50 50
a After optimization, the molar ratio of tolane to (PhP), was set at 1.20.
complexes of la.' In view of this we decided to launch a thorough study of this ring. Special attention has been paid to possible electronic delocalization and to the consequences of cyclic strain.
3
lb
( 1)
(4)(a) A. H.Cowley and K. E. Hill, Zmrg. Chem., 12,1446(1973). (b) While this manuscript waa in the hands of the referees a new eyntheaia of the diphoephetene ring appeared in the literatwe;it relies upon the reaction of oxalyl chloride with bia(trimethyMly1)phoephinee; the yields are high but only diphoephetenea with R' = OS M i e can be obtained: R. Appel and V. Barth, Tetruhedron Lett., 21, 1923 (1980). (5) F. Mathey, Tetrahedron, 28,4171 (1972).
corresponding triphospholene 2e was not detected. Obviously the steric bulk of the tert-butyl groups favored formation of the diphosphetene ring; this point will be discussed again in the next section. By contrast with 3-hexyne, the only fully characterized nonpolymeric product which was obtained was the triphospholene 2c, and we were unable to identify the expected diphosphetene IC.
In fact by chromatography on silica gel we isolated a product which was eluted before 2c (as expected for IC) but whose NMR spectrum showed ethylenic protons around 6 ppm exactly as if migration of the double bond had taken place from an endo- to an exocyclic position. We did not study this product further. However, at this point it was clear that the direct synthesis of the diphosphetene ring by reaction of cyclopolyphosphines with alkynes was of limited scope and seemed to be restricted to compounds substituted either by bulky or by electronwithdrawing R1groups. Another synthesis of the diphosphetene ring was thus obviously needed. The triphospholene system was a logical starting point for that purpose since on the one hand it was generally by far the main product of the reaction of polyphosphines with alkynes and since on the other hand Baudler et al.6 had shown that such species were also among the main products of the reaction of cis-1,Bdichloroalkenes with the dianions obtained by alkali metal cleavage of cyclopolyphosphines. Thus we decided to study the conversion of triphospholene 2b into diphosphetene lb. We chose the following approach. The triphospholene 2b was reacted with 4 equiv of lithium in THF at rmm temperature (eq 2). The resulting mixture Ph
was then reacted with a stoichiometric amount of phosgene. We thus obtained the expected diphosphetene l b contaminated with the starting triphospholene 2b. The overall yield of lb was 25%. We checked separately by 'IZC that the lithium cleavage was quantitative and that 2b was re-formed during the final step. We then observed that when the lithium to magnesium exchange was performed by reacting MgBrz with the mixture of lithiophosphines before addition of phosgene, the re-formation of 2b was minimized,and the diphosphetene yield reached 43%. Finally, by using the first procedure, we were able to obtain the unknown diphosphetene IC in 22% yield when starting from triphospholene 2c. Then we attempted to prepare the Arst C-unsubstituted diphosphetene, Id. For that purpose we synthesized at first the corresponding unknown tri(6)M. Baudler and E. Tob, 2.Naturforsch., B Anorg. Chem., Org. Chem., 33B, 691 (1978).
J. Org. Chem., Vol. 46, No. I, 1981 5
1,2-DiphospheteneRing
Figure 1. Structure of lb. Table 11. Final Atomic Coordinates ( X 104)a atom
X
P
3739.7(1.0) 3173 (3) 4077(4) 5021 (4) 5319(4) 4678(5) 3745 (5) 3439(4) 4040(4) 5581 (4) 6395(4) 5688 (5) 4161 (5) 3355 (4)
C C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12)
z
Y
2605.6 (0.6) 2711 (2) 3751 (2) 3851 (3) 4701 (3) 5461 (3) 5380 (3) 4527 (2) 3115 (2) 3160 (3) 3552 (3) 3913 (3) 3896 (3) 3499 (3)
7527.7(0.6) 6438 (2) 7909 (2) 8592 (2) 8920 (2) 8586 (3) 7910 (3) 7570 (3) 5761 (2) 5798 (2) 5165 (3) 4482 (3) 4438 (2) 5067 ( 2 )
Figure 2. Packing in unit cell of lb.
,c:
Estimated standard deviations in parentheses. Figure 3. Newman projection along the P-P bond of lb. Table 111. Bond Lengths ( A ) with Esd’s
P-c P-C(1) P-P c-C(7)
1.830(3) 1.814(4) 2.248(1) 1.464(5) 1.358(4) 1.394(5) 1.387(5) 1.381(6) 1.365(6)
c-c
C(l)-C(2) C(l)-C(6) C(2)-C(3) C(3)-C(4)
C(4)-C(5) C(5)-C(6) C(7)-C(8) C(7)-C( 12) C(8)-C(9) C(9)-C(10)
C(lO)-C(ll) C(ll)-C(12)
1.376(6) 1.394 (5) 1.386 (5) 1.393 (5) 1.378(6) 1.373 (6) 1.373 (6) 1.372(5)
phospholene 2d by using the method described by Baudlel.6 for the analogous P-Me derivative (eq 3). K,(PPh),
-c’ \cI /‘-
t H\ CI
THF - 4 0 to t20
2d (yield 21%) (3) O C
Unfortunately all our attempts to convert 2d into Id by the procedure which was successfully used for the conversion of 2b and 2c into l b and IC failed. The only recovered product was always 2d itself, suggesting a very low stability for Id (see the following section for a tentative explanation). Crystal Structure of 1,2,3,4-Tetraphenyl-1,2-diphosphetene (lb). Figure 1 shows the structure of the molecule. Figure 2 shows the packing in the unit cell. The final coordinates, bond lengths and angles are given in Tables II-IV. The molecular geometry of l b is governed by its Czsymmetry. The cycle is not planar: if we name MPP and MCC the middle points of the bonds P-P and C=C, then the dihedral angle P-MPP-MCC-C is 19O. The lone pairs of the P atoms are pointing to both sides of the four-membered cycle. The conformation of the P-P subunit is more precisely illustrated in Figure 3 by a Newman projection along the P-P bond. The approximately semieclipsed conformation very similar to that of tetracyclohexylbiphosphine7is clearly unfavorable for an
Table IV. Interbond Angles (deg) with Esd’s
c-P-C(1) c-P-P C(1)-P-P P-c-C(7) P-c-c C(7)-c-c
106.9(1) C(4)-C(5)-C(6) 74.7(1) C(l)-C(6)4(5) 107.0(1) C-C(7)-C(8) 126.7(2) C-C(7)-C(12) 102.1(2) C(8)-C(7)-C(12) 131.2(3) C(7)-C(8)-C(9) P-C(l)-C(B) 117.7(3) C(8)-C(9)-C(lO) 124.1 (3) C(9)-C(lO)-C(ll) P-C(l)-C(G) C(2)-C( 1)-C( 6) 118.2(3) C(lO)-C(11)-C( 12) C(l)-C(2)-C(3) 120.9(4) C(7)-C(l2)-C(ll) C(2)-C(3)-C(4) 120.5(4) C(3)-C(4)-C(5) 119.8(4)
120.4(4) 120.2(4) 121.3(3) 121.6(3) 117.1 (3) 121.2(4) 120.3(4) 119.7 (4) 119.8(4) 121.8(4)
aromatization of the molecule. This lack of aromaticity is also supported by the following observations: the C = C bond length [1.358 (4) A] does not differ significantly from that found in cis-stilbene [1.334 (15) A];s the P-C (cycle) bond length [1.830 (3) A] is very close to the sum of the covalent radii of phosphorus and carbon (1.84 A) and is even longer than the P-Ph bond length [1.814 (4) A]. These results are in good agreement with the conclusions that Cowley et al? drew from a photoelectron spectroscopic study of la as illustrated by the following quotation: “It is interesting that only one lone pair signal was obtained from la. This could be due to orthogonality of the two phosphorus lone pair orbitals, combined with a negligible coupling to the C=C ?r MO”. The other problem of interest is centered on the cyclic strain within the diphos(7)Von R. Richter, J. Kaiser, J. Sieler, H. Hartung,and C. Peter, Acta Crystallogr., Sect. B, B33, 1887 (1977). (8) M.Traetteberg and E. B. Frantsen, J.Mol. Struct., 26,69(1975). (9)A. H.Cowley, M. J. S. Dewar, D. W. Goodman, and M. C. Padolina, J. Am. Chem. Soc., 96,3666(1974).The lack of cyclic delocalization in diphosphetenes is also suggested by an ESR study of the anion radical of la: T. C. Wallace, R. West, and A. H. Cowley, Inorg. Chem., 13,182 (1974).
6
J. Org. Chem., Vol. 46, No. 1, 1981
Charrier, Guilhem, and Mathey
Table V. 31PNMR Data" of Diphosphetenes and Triphospholenes R R' no. 3' P J(P-P )
ref
la lb
-40 2 CF3 CF3 Ph Ph -37.5 this work Ph Et IC -32.2 this work R/p-p R' Ph t-Bu le -51.4 this work CF, CF3 2a AB,: V A - 4 1 220 2 R' V B 55 /\ Ph Ph 2b V A -52.2 250.6 this work I U B 47 Ph Et 2c v A -44.8 242.5 this work V B 41.5 Ph H 2d u A -25.2 256.4 this work V B 29.8 Me H V A -68.0 236 6 V B 11.3 values; J values in hertz; 85%H3P0, as external reference; positive values are for downfield shifts.
R'x
1 .
In 6
phetene ring. The geometry of the C=C double bond is strongly distorted as shown by the values of the P h - C = C [131.2 (3)O] and P - C = C angles [102.1 (2)Oj. In the same way the geometry of the P-P subunit is also distorted. The P-P bond length [2.248 (1) A] is longer than usual for a biphosphine: Me4P2,2.192 (9) A;'O (C6H1J4P2,2.215 (3) A.7 The bond angles around phosphorus also deviate from the normal values: in lb, P-P-C (cycle) = 74.7 (1)O, PP-Ph = 107.0 (1)O;in gazeous Me4P2,P-P-C = 101.1 (7)";'O in crystalline (C6Hll)4P2,7P-P-C = 100.6 (3), 101.8 (3), 107.4 (3), and 108.0 (3)". Clearly there is no significant distorsion of the P-P-Ph angle in lb, but, conversely, a drastic decrease of the P-P-C (cycle) angle is observed. From all these observations it appears that the diphosphetene ring is highly strained. At this point one question arises: if the four-membered cycle is very strained and if no electronic stabilization (aromaticity) operates within the ring, then why are diphosphetenea stable? We suggest two explanations: on comparison of the structure of cisstilbene8 with that of the PhC=CPh subunit in lb, it appears that practically no additional distorsion of the geometry of the double bond occurs when going from cis-stilbene to lb: PhC=C = 129.5 (7)" in cis-stilbene; Ph-C=C = 131.2 (3)O in lb. Thus it seems that C-substituents play a key role in the stability of the C2P2cycle by "preforming" the needed C = C double bond geometry. Such an explanation is of no value for the Ph-P-P-Ph subunit. However, it must be remembered at this point that theoretical calculations have brought convincing evidence in favor of P-P bent bonds in the P4molecule.lla Phosphorus is able to minimize the strain by using its 3p orbitals. A similar explanation can be used for lb. If this is the case, then the s character of the lone pairs on the phosphorus atoms of lb is high, and some chemical consequences can be expected (for example a low basicityllb). A t the end of this section comment is made on the structure of triphospholenes 2b-d. The 31PNMR data (Table V) and especially the magnitudes of the 'J(P-P) coupling constants imply the "all-trans" structure as already discussed in ref 6. Chemical Reactivity. Ecker and Schmidt described only the reactions of lb with S8 and H2OP3 We have completed their data by studying the reactions of lb with lithium and iron carbonyls.
Lithium in THF at room temperature cleaves the P-P bond of 1b, but the reaction is more sluggish than with the corresponding triphospholene 2b (ea. 4). By reaction of the dilithio compound thus obtained first with methyl iodide and then with sulfur, the two diastereokomeric "cis" disulfides 5 were obtained in 89% combined yield. lb
f
2Li
THF
Ph
Ph
PhP
Li
ii
5
The dilithio compound also reacted with MePC12 or MeP(S)C12to give the corresponding triphospholene 6 in 35% yield (eq 5). The desulfuration which took place in
'Wh
PhP
PPh t MePC12 or MeP(S)C12
\LI LI/
wPh
Ph
Me
6
the second case suggests that the central phosphorus of triphospholenes has a low nucleophilicity in the tervalent state. This suggestion is supported by the observation of Ecker and Schmidt3that reaction of 2b with S8gives the l,&disulfide exclusively. At room temperature l b reacted with Fe(CO)4.THF12 to give a very unstable P+Fe(C0)4 complex 7, which was
phwph Ph
7
(10)A. McAdam, B.Beagley, and T. G . Hewitt, Trans. Faraday SOC., 66, 2732 (1970). (11)(a) See for example: M. F. Guest, I. H. Hillier, and V. R. Saunders, J. Chem. SOC.,Faraday Trans. 2, 68, 2070 (1972). (b) For a correlation of the basicity with the s character of the lone pair in Pm compounds, see H. Goetz, G. Frenking,and F. Mmhner, Phosphorus Sulfur, 4,309 (1978).
only characterized by its IFt spectrum (cyclohexane): uCo 2050 (s), 1980 (s), 1950 cm-l (vs). The spontaneous decomposition of 7 gave back lb, and thus we know that the (12)F.A. Cotton and J. M. Troup, J. Am. Chem. Soc., 96,3438(1974).
1,2-DiphospheteneRing
J. Org. Chem., Vol. 46, No. 1, 1981 7
Table VI. Reaction of l b with Iron Carbonyls reagent exptl conditions product (yield, %) Fe3(C0
8 (5),9 + 10 (60) 8 (5),9 (40) 8 (5119 (3),10 (75) 8 (5h9 (la), 10 (55)
90 OC, 1 h 140 'C, 18 h
Fe3(C0)12 112
80 'C, 5 h
Fe,(CO),
110 OC, 5 h
Fe,(CO),
calculate a 31Pshift of 152.8 ppm for 9; the observed value is 152 ppm (C&).
diphosphetene ring is retained in 7. By analogy with the corresponding complex of la: we assume that 7 is a mono complex. From the IR data it is obvious that the donor strength of lb is closer to that of Ph3P13than to that of ia.4
The reaction of lb with FezCO9or Fe3(C0)12a t higher temperature was much more interesting. Three complexes (8-10) were obtained (numbered according to decreasing R j s in chromatography). Some experimental data are collected in Table VI. The following points are noteworthy: at 150 "C in xylene, 10 was converted into 9 in
Q 6,,
Ph
P ',P
h
12, X = PPh, Fe,(CO),
The structure of 9 allows the easy visualization of ita reaction with Fe2(COIgwhich leads to 8 by simple replacement of the Ph2C2 by a Fe(C0)3 subunit (eq 6). (OC)3Fe------
F\/(c0)3 PzPhz [Fe(CO)$ C2Ph2
-c
12
9 Ph
I
Fe(CO)3
(OC )SF',------
Ph
/I
8 Ph /
P
I
b'/
'Ph
9
Ph
8 /PRz
(OC ),Fe----->Fe(C0)3 P 'R
2'
11
75% yield; within 2 h at 150 "C in xylene, 9 reacted with Fe2(C0)9to give 8 quantitatively; within 6 h at 150 "C in xylene, 10 reacted with Fe2(COI9to give 8 in only 50% yield together with 9 and 10. These data indicate that 10 is the primary product around 80 "C whereas 8 is the final product around 150 "C if an excess of iron carbonyl is wed. Complex 8 was easily identified since it has been previously described.14 Its formula corresponds to the loss of the tolane subunit in lb. Its most characteristic feature is its very low field 31Presonance: dslp of 8 316.3 (see ref 15). The structure of 9 was established beyond any doubt by elemental analysis and spectroscopy. Mass spectroscopy and elemental analysis indicate a LFe2(CO)6formulation (L = lb). The cleavage of the P-P bond is shown by the close similarity of the IR and 31Pand 13C NMR spectra to those of various authenticated phosphidobridged complexes 11: IR for 9 v(C0) 2055 (m), 2015 (s), 1995 (s), 1970 (s), 1960 cm-l (w) (cyclohexane);for 11 (PR, = P(Me)Ph sym)16v(C0) 2055 (m), 2017 (s), 1996 (m), 1968 (m), 1960 cm-' (w) (heptane); 13CNMR for 9 d(C0) 212.9 (C&); for 11 (PR2 = PMe2)" d(c0) 212.7. A large downfield shift of the phosphorus resonance (105.8ppm) was observed when converting 12 with X = PPh into 12 with X = Fez(C0)6.18 Thus, from the 31Pdata of 2b we
Unfortunately we have been unable to establish the structure of the primary complex 10. The mass spectrum is very similar to that of 9, but this indication is of no use since 10 is converted into 9 upon heating. The C, H, and P analysis seems to indicate a LFez(C0)6formulation, but the lower accuracy of the resulta cast some doubt upon this hypothesis. The 13C NMR, 31PNMR, and IR data are given in the Experimental Section but give no clue for our problem. Investigations on the synthesis and chemistry of diphosphetenes are continuing. Experimental Section
All reactions were performed under an argon atmosphere. Sica
gel and solvents were used after being degassed with argon. Molecular weights were measured on a AEI-MS-30 mass spectrometer at 70 eV. 'H NMR spectra were recorded on a R24A Perkin-Elmer spectrometer. 31Pspectra were run on a WP 90 Bruker spectrometer; 31Pchemical shifta are externally referenced to 85% H3P01and are positive for downfield shifts. IR spectra were recorded on a Perkin-Elmer Model 297 spectrometer. Reaction of Acetylenic Compounds with Pentaphenylcyclopentaphosphine. A mixture of acetyleniccompound and pentaphenylcyclopentaphosphine (molar ratio 6:5)was heated in a sealed tube. The yellow oil thus obtained was chromatographed on a silica gel column (50g of silica gel/g of product) prepared in benzene-hexane (1:4).Results are given in Table VTZ. %action Of L ~ P ( C B H ~ ) P ( C ~ H ~ ) P ( Cwith ~ H ~cis-Di)L~ chloroethylene. A 0.212-gsample of lithium and 5 g of (C,@$)s were stirred for 5 h in 50 mL of THF. The mixture was cooled at -40 "C, and 1.55 g of cis-ClCH=CHCl was added dropwise. The mixture was stirred for 15 h at room temperature. The solvent was evaporated, and the residue was chromatographed through a silica gel column prepared in benzenehexane (1:4).Two producta were recovered. 1,4Diphenyldihy&o-l,4diphosphorin: 0.06 g (2.5% yield);mp
(13)A. Reckzeigel and M. Bigorgne, J. Organomet. Chem., 3, 341 (1965). .~~ ~ . , (14)P.M.Treichel, W. K. Dean, and W. M. Douglas, Znorg. Chem., 11, 1609 (1972). (15)J. P.Lampin and F. Mathey, C. R. Hebd. Seances Acad. Sci., Ser. C, 282,979 (1976). (16)P.M.Treichel, W. M. Douglas, and W. K. Dean, Inorg. Chem., 11, 1615 (1972). (17)R. D. Adams, F. A. Cotton, W. R. Cullen, D. L. Hunter,and L. Mihichuk, Znorg. Chem., 14, 1395 (1975).
82 "C; mol wt 268; 'H NMR b 7.1-7.7 (m, 10 H, phenyl), 6.3 (t, J P =~22 Hz, 4 H ethylenic);31PNMR 6 -43.8.Anal. Calcd C, 71.64;H, 5.26;P, 23.10. Found: C, 71.50; H, 5.06; P, 23.06. l,P,B-Triphenyl-1,2,3-triphospholene (2d): 1.12 g (21% yield); mp 79 "C; mol w t 350. Anal. Calcd C,68.58;H, 4.89; P,26.53. Found: C, 68.05;H, 4.59;P,26.40. (18)R. B. King and R. H. Reimann, Inorg. Chem., 15, 184 (1976).
8 J . Org. Chem., Vol. 46, No. 1, 1981
Charrier, Guilhem, and Mathey
- - ________
I _
temp, t , acetylenic compd C,H,C=CC,H,
"C 240
h
C,H,C=CC,H,
170
72
(CH,),CC=CC(CH,),
170 48
a
Table VI1 diphosphetene triphospholene anal. found anal. found mp, (calcd) mass yield. (calcd) mass .. "C . % mp. "C 159 C, 78.91 (79.19) 394 50 (2b) 129 C, 76.62 (76.49) 502 H, 4.97 (5.08) H. 4.74 (4.98) P, 15.63 (15.74) P,' 18.50 (18.52) C. 70.58 (70.93) 406 37 (2c) oil Hi 6.02 (6.15)' P, 22.67 (22.90) 115.5 C, 74.74 (74.56) 354 0 (2e) H, 8.07 (7.96) P,. 17.45 ji7.5i)
6
yield, . . % 15 ( 1 b ) O 0
(IC)
30 ( l e )
Also pentaphenylphosphole 4: mp 257 "C;mol wt 464;2% yield
Synthesis of Diphosphetenes from Triphospholenes. A 5-"01 sample of triphospholene in 100 mL of THF and 20 mmol of lithium were stirred together for 15 h. The mixture became reddish black with pentaphenyltriphospholene (2b) and red with 1,2,3-triphenyl-4,5-diethyl-1,2,3-triphospholene (2c). When the lithium had disappeared, 20 mmol of MgBr2was added. After 1 h, 10 mmol of phosgene in toluene (20%) was added dropwise a t room temperature. The mixture was stirred again for 2 h, the solvents were evaporated, and the residue was chromatographed through a silica gel column prepared in benzene-hexane (1:4). 1,2,3,4-Tetraphenyl-1,2-diphosphetene (lb) was obtained by this method in 43% yield. On the other hand, without MgBr2, 1,2diphenyl-3,4diethyl-l,2-diphosphetene (IC) was obtained in 22% yield as a colorless oil: mol wt 298;'H NMR 6 7.3 -7.6 (m, 10 H,phenyl), 2.3 (m, 4 H, methylene), 1.0 (t, 6 H, methyl, 3 J m = 7 Hz). Anal. Calcd C, 72.41;H, 6.76;P, 20.83. Found: C, 72.30; H, 6.42;PI 20.57. Attempts to Prepare 1,2-Diphenyl-1,2-diphosphetene.The reaction of 5 mmol of 2d with 20 mmol of lithium in 100 mL of THF was not complete after 15 h. Only 50% of the lithium had reacted. With potassium, 75% of the metal had reacted. The reaction was complete when the sodium-naphthalene anion radical was used. A 0.145-gsample of sodium and 0.850 g of naphthalene in 70 mL of THF were stirred for 5 h, 1.5 mmol of 2d was then added, the mixture was stirred again for 15 h, and 2 g of MgBrz was added. The dark red reaction medium immediately became yellow and transparent. C0C12(3mmol) in toluene (20%) was then added at room temperature. The mixture was stirred for 1 h. The only main product recovered after chromatography was 2d (-20%). Chemical Reactivity of Tetraphenyldiphosphetene.Reaction of Diphosphetene with Lithium. A 2.36-gsample of diphosphetene lb (6mmol) and 0.084g of lithium (12mmol) in 100 mL of THF were stirred at room temperature for 15 h. ICH3 (1.7g, 12 mmol) in 20 mL of THF was added dropwise to the reddish black solution. The mixture was stirred for 2 h, and 0.4 g of sulfur was added. The solution was stirred overnight. The solvent was evaporated, and the residue was chromatographed through a silica gel column prepared in hexane. The excess sulfur was thus recovered; the column was then washed with etherhexane (2:1),and 2.6 g of two solid diastereoisomers of (CGH~)(CH~P(S)C(CGHHS)=C(CGH~P(S)(CGHH~CH~ (5,8970yield) was recovered: mol wt 488;'H NMR 6 6.5-8 (m, 20 H, phenyl), 1.8(d, JPH = 13 Hz, 6 H,methyl, first diastereomer), 1.7 (d, JPH = 13 Hz, 6 H, methyl, second diastereomer). Anal. Calcd: C, 68.83;H, 5.36. Found C,68.79;HI 5.10. A 0.234-gsample of CH3PC12(2mmol) in 5 mL of THF was added at -20 "C to a solution of 2 mmol of the dilithio compound prepared with 0.790 g of l b and 0.028 g of lithium in 50 mL of THF. The mixture was stirred for 3 h and warmed from -20 "C
to room temperature. The solvent was removed, and the residue was chromatographed with benzene-hexane (1:4)to give 0.310 g (35% yield) of 1,3,4,5tetraphenyl-2-methyl-1,2,3-triphospholene (6): mol wt 440;'H NMR 6 6.6-7.8 (m, 20 H, phenyl), 1.45 (dt, 3 H, methyl, VPH= 6.5 Hz,VPH= 16 Hz).Anal. C a l d C, 73.63; H, 5.23. Found: C, 73.2;H, 4.9. The same reaction was performed with 0.3 g of CH3P(S)C12, and 0.180 g (20% yield) of 6 was recovered. Reaction of Diphosphetene with Fe(CO)4.THF. Fe(CO),-THF was prepared as in ref 12 from Fe2(CO)9(1g) in THF (100mL) under a CO atmosphere. Diphosphetene l b (200mg) was then added, and the mixture was stirred at room temperature (3h). The solvent was removed, and the residue was chromatographed through a silica gel column prepared in benzenehexane (1:4).Complex 7 was recovered (0.2g, 71 % yield). It was unstable and gave back diphosphetene l b after some hours at room temperature. Reaction of Diphosphetene with Fe2(CO)9and Fe,(CO)lz. A 0.394-g(1mmol) sample of l b and 1.2 mmol of iron carbonyl in 50 mL of xylene were heated together. The solvent was evaporated,and the residue was chromatographed through a silica gel column prepared in benzene-hexane (1:4).Three complexes were recovered. Their ratios were dependent on experimental conditions (see Table VI). Complex 8: (C6HSP)2Fe3(CO)9; mp 135 "c;mol wt 636;31P NMR 316.3. Complex 9: (C6H~)2P2C2(C6H5)2Fe2(C0)6; mp 206 "c (after recrystallization in pentane); mol wt 674;IR (cyclohexane)Y(W) 2055 (m), 2015 (s), 1995 (s), 1970 (s), 1960 cm-' (w); 31PNMR 6 152. Anal. Calcd C, 57.01;H, 2.99;Fe, 16.62;P,9.20. Found: C, 57.07;H, 3.07;Fe, 16.72;P, 9.18. Complex 10 (C$15)2P2C2(C6H5)2Fe2(co)~; mp 139.5 "C (after recrystallizationin pentane); IR (cyclohexane) qco)2060 (m), 2050 (s), 1980 (s), 1960 (vs), 1947 cm-'(8); 31PNMR 6 107. Anal. Calcd (for n = 6): C, 57.01;H, 2.99;P, 9.20.Found: C, 57.06;H, 3.12; P, 9.50. Registry No. la, 2375-86-2; lb, 42451-95-6; IC, 75600-53-2; le, 75600-54-3;2a, 2546-25-0;2b, 75600-55-4;2c, 75600-56-5;2d, 75600-57-6; 2e, 75600-587; 4,1181-62-0; 5 (isomer l),75600-59-8; 5 (isomer 2),75625-41-1; 6,75600-60-1; 7,75625-86-4; 8,38903-71-8; 9, 75625-87-5; 11 (PR2 = P(Me)Ph), 75684-20-7;11 (Prz = PMe2), 14871-43-3; cis-dichloroethylene, 156-59-2; 1,4-diphenyldihydro-1,4diphosphorin, 75600-61-2;tolane, 501-65-5;3-hexyne, 928-49-4; 2,2,5,5-tetramethyl-3-hexyne, 17530-24-4; Li(c$I,)P(c$IH,)P(c6H5)Li, 22961-05-3;Fe(CO)4THF,52268-67-4;Fe2(CO)B,15321-51-4; Fe3(C0)1z, 17685-52-8. Supplementary Material Available: Observed and calculated structure factors (F, and F3 (6pages). Ordering information is given on any current masthead page.
